HP 1905 No power. No led. No output voltage.

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

jetadm123, thanks for the inputs.. just a quick updates below,..
p/s- i may not have all the answers to all the questions above.. but i will try my best to answer them..

1) Glad to know & hope so it lasts, because that is my last IC.. i am not sure whether i busted the one i replaced earlier while soldering it.

2a) Currently i have not have the chance to assembled them back as i want to prioritize the taking of the logic card photo. But as far as i can recall, i can see no image.

2b) I tried scanning with my untrained eye but could see none also.

2c) Pins 5, 6, 7 & 8 of Q701 are all shorted (0.08ohms) to each other. Same goes with Q705. But i guess they should be shorted, because from schematic they are tied to the common Pins 1, 3 & 5 of PT701. Same goes with PT702. Right?

2d) Photos as attached. Note on the bottom side there is some stain which is flux.
Ok, i hope u can confirm this.
U301 (AIC1084-18cm)
Pin 1-2 = 81.3 ohms, the rest of the pins are not shorted (brief flash of reading then open)
U302 (AIC1084-33cm)
Pin 1-2 = 4.5 ohms, the rest of the pins are not shorted (brief flash of reading then open)

so are they shorted?. fyi, i continue measuring resistance across the electrolytic caps & all of them (except C401) are having the reading of either 81.3ohms or 4.5ohms. I tried removing one of them (C309) (that's where the flux came from) & measure on the pad. It shows the same with the caps off as well. Anyway i replace it since i have a spare. Not sure what's the logic or whether it is significant?

2e) same answer as 2a. AFAIK none.

3) geez!.. my bad. Probably i hook to the wrong Gnd, i guess.



PlainBill, true. When i disassembled it i need to remove the panel switch/pcb board. But upon testing i need to fix back because the on-off switch is located over there.. I hope i am understanding what you mean & answering it correctly.. Talking about multitasking.. I am now watching a cooking program with the other half while typing this, lol.. ok, off for my showers now..

To test the mosfets Q701 and Q705 for shorts:

With your DMM set to resistance and referring to the schematic :

On Q701, place one probe on S1 and the other probe on G1, record measurement, reverse probes, record measurement.

Testing should look like this:


S1-G1
D1-G1
S1-D1
S2-G2
D2-G2
S2-D2


Perform same test on Q705


To test regulators you must reassemble everything.

Looking at the regulator with the metal tab on top and numbering the pins from left to right as 1-3:

pin1 = ground
pin2 = Vout
pin3 = Vin

Power up system and measure output voltage for each regulator.

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

To test the mosfets Q701 and Q705 for shorts:

With your DMM set to resistance and referring to the schematic :

On Q701, place one probe on S1 and the other probe on G1, record measurement, reverse probes, record measurement.

Testing should look like this:


S1-G1
D1-G1
S1-D1
S2-G2
D2-G2
S2-D2


Perform same test on Q705


To test regulators you must reassemble everything.

Looking at the regulator with the metal tab on top and numbering the pins from left to right as 1-3:

pin1 = ground
pin2 = Vout
pin3 = Vin

Power up system and measure output voltage for each regulator.

With DMM set to 2000, here are the measurements:
On Q701,
S1-G1 No reading (same with reverse probing)
D1-G1 No reading (same with reverse probing)
S1-D1 Rising value until it goes to no reading (same with reverse probing)
S2-G2 No reading (same with reverse probing)
D2-G2 No reading (same with reverse probing)
S2-D2 Rising value until it goes to no reading (same with reverse probing)
The result is the same with Q705.

I reassembled the monitor except connecting the panel signal cable & measure the output voltage of the 2 regulators. here are the measurements :
U301 is 1.8V and U302 is 3.3V

I manage to also detect that 3.3V is also present on the on/off switch. But still no Power Led lighting up even if i depressed the on/off switch & of course still no backlight . So anybody have any suggestion where do i go on from here?.

[PlainBill]

Re: HP 1905 No power. No led. No output voltage.

With DMM set to 2000, here are the measurements:
On Q701,
S1-G1 No reading (same with reverse probing)
D1-G1 No reading (same with reverse probing)
S1-D1 Rising value until it goes to no reading (same with reverse probing)
S2-G2 No reading (same with reverse probing)
D2-G2 No reading (same with reverse probing)
S2-D2 Rising value until it goes to no reading (same with reverse probing)
The result is the same with Q705.

I reassembled the monitor except connecting the panel signal cable & measure the output voltage of the 2 regulators. here are the measurements :
U301 is 1.8V and U302 is 3.3V

I manage to also detect that 3.3V is also present on the on/off switch. But still no Power Led lighting up even if i depressed the on/off switch & of course still no backlight . So anybody have any suggestion where do i go on from here?.

What is the part number for U202 (right side, just above the crystal)?

PlainBill

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

What is the part number for U202 (right side, just above the crystal)?

PlainBill

Marking on it is = AL W H..
I do not know whether this will be helpful but I measured resistance on it.
With the marking upright facing me, Pin 1 is on the left, Pin 2 on the top & Pin 3 is on the right.
DMM set to 20k ohms
Pin 1-2 = 9.73k ohms; reversing the probe > 9.92k ohms
Pin 2-3 = 16.51k ohms; reversing the probe > 16.63k ohms
Pin 1-3 = 6.71k ohms; reversing the probe > 6.73k ohms

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

Good catch PlainBill. I took a quick look at the schematic and U202 looks to be a reset controller. Unfortunately, no part number is listed.

Newbie1, for your info, this could be the source of your problem. Please read the thread below starting at post #18. It affects some Viewsonic and Acer models, but it looks like it also affects you.

https://www.badcaps.net/forum/showth...set+controller

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

Good catch PlainBill. I took a quick look at the schematic and U202 looks to be a reset controller. Unfortunately, no part number is listed.

Newbie1, for your info, this could be the source of your problem. Please read the thread below starting at post #18. It affects some Viewsonic and Acer models, but it looks like it also affects you.

https://www.badcaps.net/forum/showth...set+controller

Wow! thanks guys.. will follow the steps of post#20 to test the reset controller U202.. will update again once completed.. hope it will be soon, else you know where i will be heading.. *GULP!*..

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

Ok. Nothing got burnt.. lol!..

However, all i get while shorting the 2 bottom pins was a brief flash of blue Power led lighting up.. I did pressed the on/off switch a few times while shorting the pins but the Power led never stay lighting up.. so i unplugged the monitor..

One thing i notices after doing this, was if i were to plug the monitor again & switch ON the MAIN plug, there is a brief flash of blue Power led lighting up just like shorting the reset controller even without pressing the on/off switch. Can't remember seeing it previously.. Hope my explanation is clear to you guys..

So is the reset controller faulty?.

I am worried if it is.. Looking at the cramped spaces on the logic card, I am not having great confidence unsoldering/soldering it especially without the assistance of CHIP-QUIK.

p/s: just to add, i did this with the panel facing down, hence i could not confirm whether there is a flash of light on the backlight as well.

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

Actually, I should have more specific. I wanted you to read what was on the link to familiarize yourself with what I was talking about. Since we haven't been verify it's the same chip, it would have been bad if the bottom two legs were ground and vcc when you shorted them. Whew! If your chip is similar to the MAX810, then the top leg (by itself) should be Vcc and should measure 3.3V. Bottom left leg should be Ground and right leg should be Reset. Try measuring for Vcc.

PlainBill, at this point do you think he should:

1) just replace U202?

2) try lifting the reset leg off it's solder pad and leave it floating and see what happens?

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

I downloaded the spec sheet for the MAX810. If you look on page 5, it looks like the "AL" stamped on your chip corresponds to a MAX810R with a 2.63V threshold voltage.

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

Actually, I should have more specific. I wanted you to read what was on the link to familiarize yourself with what I was talking about. Since we haven't been verify it's the same chip, it would have been bad if the bottom two legs were ground and vcc when you shorted them. Whew! If your chip is similar to the MAX810, then the top leg (by itself) should be Vcc and should measure 3.3V. Bottom left leg should be Ground and right leg should be Reset. Try measuring for Vcc.

PlainBill, at this point do you think he should:

1) just replace U202?

2) try lifting the reset leg off it's solder pad and leave it floating and see what happens?

.. I measured the voltages on the legs
Bottom left = 0V
Top = 4.94V
Bottom right = 3.97V

whoa! I thought removing the U202 would be a tough-dog but option 2 would be suicidal if i am not careful.. lol!. Ok then, i will wait for what you guys think is a better option. And thanks for providing the datasheet.

[PlainBill]

Re: HP 1905 No power. No led. No output voltage.

MAX801R has a totem pole output with an active high reset function. In other terms, when the system is powered up, the output stays at Vcc until 140 msec after Vcc rises above 2.63V. At that time it should drop to 0 volts. Therefor the reset controller is bad.

The problem now is I have no idea if the GM5321 has an internal reset controller or not. If it does, the monitor could be repaired by removing U202. If it doesn't, and the RESET input has an internal pull-up the monitor won't work, but nothing will be damaged. If there is no pull-up (or pull-down), the GM5321 could fry. So the best choice is to replace the reset controller.

[bonney]

Re: HP 1905 No power. No led. No output voltage.

pin 178 is the reset goes to U202

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

:

whoa! I thought removing the U202 would be a tough-dog but option 2 would be suicidal if i am not careful.. lol!. Ok then, i will wait for what you guys think is a better option. And thanks for providing the datasheet.

Since replacing U202 seems to be the option, you can use ChipQuik, or if you have a fine sharp pair of diagonal wire cutters, you can cut through each leg of U202 and remove the chip. Then, with your soldering iron and a pair of pliers or tweezers remove each leg.

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

MAX801R has a totem pole output with an active high reset function. In other terms, when the system is powered up, the output stays at Vcc until 140 msec after Vcc rises above 2.63V. At that time it should drop to 0 volts. Therefor the reset controller is bad.

The problem now is I have no idea if the GM5321 has an internal reset controller or not. If it does, the monitor could be repaired by removing U202. If it doesn't, and the RESET input has an internal pull-up the monitor won't work, but nothing will be damaged. If there is no pull-up (or pull-down), the GM5321 could fry. So the best choice is to replace the reset controller.

PlainBill, thanks again for the explanation & guidance. I will try to source & replace MAX810R. However, if i cannot find MAX810R locally, may i know is it workable to be replaced by MAX810S (Reset Threshold=2.93V)?

Since replacing U202 seems to be the option, you can use ChipQuik, or if you have a fine sharp pair of diagonal wire cutters, you can cut through each leg of U202 and remove the chip. Then, with your soldering iron and a pair of pliers or tweezers remove each leg.

jetadm123, thanks for the tip. As i mentioned before, i do not have ChipQuik. So i will try to follow ur method of cutting the legs first. Hope i will not damage the traces/pads as i did previously while removing the IC..

pin 178 is the reset goes to U202

bonney, noted. However, would not take the risk of lifting up the fine legs as of now.

[PlainBill]

Re: HP 1905 No power. No led. No output voltage.

Yes, the IC senses the 5V supply, so there should be no problem.

PlainBill

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

I could not find MAX810R or equivalent locally. So i am ordering them through ebay which will take about 10-20 days to arrive. I will update again once i have replaced U202, which was successfully removed as suggested on post #33.

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

I could not find MAX810R or equivalent locally. So i am ordering them through ebay which will take about 10-20 days to arrive. I will update again once i have replaced U202, which was successfully removed as suggested on post #33.

Funny, but I would have thought you would have had a lot of electronic parts to choose from because of the large amount of electronics manufacturing that goes on in that part of the world.

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

Sigh!.. Sad but true.. or maybe i have not search extensively enough,,

From what i know, those manufacturing lots do not go to the retail outlets here.. they are mainly sent to Assembly houses.. the best way i can get my hand on them quickly (within a week) are mainly through Farnell, RS components.. If not, then the next best way would be ebay, which would take painstakingly slow (10-20 days)...

So, you can imagine the mess i make in my small apartment here.. Littered with half-assembled LCDs everywhere, awaiting for parts... LOL!!..

[newbie1]

Re: HP 1905 No power. No led. No output voltage.

BAD news!. Replaced U202 with MAX810REUR ALAA. STILL DEAD. No power LED. Nothing.

-Measured 3.3V & 1.8V still present from regulators
-Measured panel having 3.3V
-Measured on Power switch, is 3.3V when not depressed but 0V when depressed
-Measured on U202; Top leg - 4.97V, Bottom 2 logs both - 0V

any suggestions what to do next?

I guess this bird is flying away & my stone might not be able to knock it down. ..

[jetadm123]

Re: HP 1905 No power. No led. No output voltage.

At this point the only thing I can think of is that the EEPROM, U205, got corrupted. According to the schematic, it's a M24C16-MN6T. IF there's a method to perform an EEPROM reset, then that's a possible solution. On some Samsung's you can just replace the old EEPROM with a blank one. I don't know how it works in your case.